The present invention relates to digital data processing, and more particularly to an improved means and method for detecting and correcting errors in a single track of data, and correcting errors in two identified erroneous data tracks.
In transporting and processing data coded into digital form, immense numbers of individual data bits must be processed at a high rate. Since each data bit uniquely contributes to the meaning of the encoded data, the erroneous detection and/or processing of even a single bit of data can result in significant errors. However, in view of the enormous number of individual bits which are to be processed, a failure with respect to one or more bits among a large number thereof is a statistical probability.
In order to insure against certain types of failures, various types of correction mechanisms have been designed. One approach is to provide redundant data processing mechanisms, and compare the outputs thereof. The disadvantages to this approach are manifest in that it requires the expensive duplication of systems. Other approaches have involved the use of error-checking codes which themselves can be so complex as to require an inordinate amount of digital data for their implementation.
Recently there has been proposed a recorded format for group coded recording 6250 bits per inch. The format of this standard requires a data group of seven data characters plus an error-checking code character, there being seven data characters. Each data character comprises one byte of eight bits, plus a parity bit. One track is provided for each bit, there being a total of nine tracks. The ECC character is formed from a seventh-order polynomial, the coefficients for each term of which comprise one of the data characters so that each data character D1-D7 is a coefficient for one of the polynomial terms. By associating the coefficients in increasing order with the polynomial terms which are arranged in decreasing order, and multiplying the sum thereof by a generator polynomial the ECC character can be created. However, while the mathematical relationship between the ECC character and the information encoded in the data bytes is known, the method of making use of the ECC character, and the means therefor, are not publicly known.
It is therefore an object of the present invention to provide a means and method for the correction of data arranged in a format according to the 6250 CPI group-coded recording proposed national standard.
It is another object of the present invention to provide improved means for making use of the error-checking code of the 6250 CPI group-coded recording proposed standard.
Still another object of the invention is to provide a means and method for detecting and correcting errors in one track of a multi-track data group using an ECC, and for correcting two erroneous tracks in such a data group in the presence of pointer values identifying the erroneous tracks.